In many application it is desirable to have an interlock mechanism so that an isolation switch cannot be operated when the contacts of an electromechanical device such as a contactor are in a closed position and electrical current is flowing to a load. Particularly, it is desirable to have an electromagnetic contactor interrupt a current flow to a load rather than to have a hand operated isolation switch interrupt the current flow to the load. It is therefore necessary to design a mechanical interlock which is responsive to the position of the armature of the contactor, and which prevents hand operation of the isolation switch.
A continuing problem in the art has been to design an interlock mechanism both responsive to the position of the armature of a contactor and arranged so that the force which can be exerted against the contactor is limited by the mechanism. For example, an operator may exert excessive force on a hand lever of an operating handle in order to try to force the contacts of the isolation switch open and thereby interrupt a load current. The excessive force exerted by the operator on the hand lever may damage or break parts of the electromagnetic contactor. The design of a force limiting mechanical linkage has been a continuing problem in the field of interlock mechanisms for electromagnetic contactors.